US President Barack Obama has sharpened his warnings about Britain’s reduced global influence in the event of it leaving the EU, warning it could take ten years to reach a UK-US trade deal.

In an interview with the BBC broadcast on the final day of his four-day visit to Britain Sunday, Obama said that Britain would have “less influence globally” if it votes to leave the EU in a June referendum.

On the prospect of Britain reaching a post-Brexit trade deal with the US, Obama said “it could be five years from now, 10 years from now before we were able to actually get something done.”

“The UK would not be able to negotiate something with the United States faster than the EU,” he said.

“We wouldn’t abandon our efforts to negotiate a trade deal with our largest trading partner, the European market.”

His comments are the latest in a series of stark warnings about the consequences of Britain ditching its EU membership that have poured fuel on an already heated debate and prompted a furious response from anti-EU campaigners.

They have portrayed Obama as meddling, and questioned whether he might be anti-British.

While some of the comments from London Mayor Boris Johnson and others have been seen as racially charged, the White House is keenly aware of the risk of being seen as interfering.

But in weighing that risk, Obama appears to have decided it is more important to pitch in and try avert a referendum defeat that being seen to not do enough.

Washington fears Britain exiting the EU would close off of a key conduit of US influence in Europe.

On his visit to Britain, during which he met Labour leader Jeremy Corbyn and played golf with Prime Minister David Cameron, both of whom back staying in the EU, Obama warned Britain would go to the “back” of the trade queue with the US if Brexit occurred.

On Sunday, Obama will continue his tour of Europe and the Gulf in Germany, where he will meet Angela Merkel.

The German chancellor is one of his closest allies on the world stage and the leader of Europe’s biggest economy.